1. Field of the Invention
Embodiments relates to voltage adjusting technology, and more particularly, to a voltage adjusting circuit to generate constant power in an external environment such as a distance between a card reader and a contactless card, a contactless card and a contactless card system which include the same, and methods of operating the voltage adjusting circuit and the contactless card.
2. Description of the Related Art
Contactless card systems, for example, smart card systems, use contactless information detection technology in which a card reader detects a smart card, which is disposed away from the card reader by a distance, and transmits and receives information to and from the smart card using a radio frequency.
A contactless card is supplied with power by inducing voltage from electromagnetic waves emitted by a card reader. Accordingly, the power induced in the contactless card changes depending on a distance between the contactless card and the card reader or the like. When the power exceeding what is needed for driving the contactless card is induced in the contactless card, an internal logic circuit in the contactless card may malfunction or break down due to the excessive power.
To overcome this problem, constant power needs to be supplied to the internal logic circuit regardless of external environments.